The invention relates to a liquid-cooled rotary piston internal combustion engine with a housing consisting of at least one annular shell with an interior guideway and two parallel end pieces and bounding an interior space. The shell and end pieces contain cavities for circulation of two cooling circuits completely separate from each other. One of the circuits cools the region of the housing in the hot arc of the shell where the ignition, expansion and exhaust strokes occur in the interior space. A liquid-cooled piston revolves in the housing.
There is a known rotary piston internal combustion engine of the kind described U.S. Pat. No. 3,921,593 where two separate cooling circuits have different temperature levels and function independantly of each other. The in general differentially heated regions of the engine are bathed with coolant in a manner that a substantially uniform heating of the housing can be achieved. The housing regions not cooled by cooling from these two circuits are cooled by the lubricant leaving the piston. This means in that arrangement that there is still another coolant circuit affecting the operating temperature of the machine. In any consideration of operating temperature, however, especially in the cold start and warm-up phase, the piston temperature also plays a very important part, as fuel consumption and engine wear will depend on it to a considerable extent. After a cold start, even the aforementioned division of the coolant flow into two independent cooling circuits cannot of itself result in any very rapid heating of the coolant. The comparatively cold lubricant introduced into the liquid-cooled piston and constituting the additional third circuit will retard a rapid rise in operating temperature owing to the comparatively large heat-transfer surface of the piston and the long lubricant heating time required on that account.